I think I already found the error. In my report suite I have two break-downs for Campaign ID, one for Tracking Code, one for eVar 21. While they should report the same, there is some discrepancy. Will check internally why this is the case.
Could you assist with the other queries maybe?
1/ It returns only 10 items of eVar21
2/ There are also entries in that list that had no visits (visits:0)
And one additional question:
3/ How do I find the ID of a custom segment in Omniture to use in the JSON Request?
Especially I'm looking for a way to only show values for eVar21 if they have had >=1 visits. Is that possible?